The present invention relates to apparatus for producing semiconductor devices, and more specifically relates to apparatus of the type for coating insulating films on a surface of semiconductor chips mounted on a lead frame to produce semiconductor device.
In general, a semiconductor device is susceptible to thermal, chemical and physical stress from the environment which causes a change of electrical characteristics thereof, thereby generating reliability problems. Especially, in the production of semiconductor devices of the plastic encapsulation type, there is observed a serious problem that a pad is corroded at a junction between an aluminium electrode of the semiconductor device and a metal lead. In view of this, after a small lead is connected between the semiconductor device electrodes and the external lead lines, a protective film is formed on the surface of the semiconductor device, the formation being made at low temperature below 400.degree. C. so as to improve moisture resistance.
Conventionally, the method of forming such a protective film includes forming a silicon oxide film (SiO.sub.2) by a vapor-deposition-method by using monosilane (SiH.sub.4) and ozone (O.sub.3) (for example, Japanese Patent Publication No. 33914/1974), and forming a silicon nitride film (Si.sub.3 N.sub.4) by vapor-deposition method with irradiating ultraviolet ray to a gas mixture of monosilane and ammonia (NH.sub.3) added with a photosensitizer composed of mercury (Hg) (for example, J. W. Peter et al. Solid State Technology, Sep. 1980, pp. 121-126).
As desclosed in the above references related to the protective film forming technology, the thin film forming apparatus is comprised of a CVD apparatus used in preceding steps of the semiconductor fabrication process, i.e., in a water production process prior to the division of the semiconductor wafer into chips. Hence, the conventional apparatus does not suitably provide for an assembling process in which lead frames mounting semiconductor chips are treated as a lot to carry out a batch process working, thereby causing a drawback in that the productive fabrication process cannot be carried out.